Calculation of coil heat exchangers with variable bending radius of a helical spiral

RELEVANCE . Due to the significant variety of configurations of heat exchange elements and designs of heat exchangers, coefficients of the criterion equation are proposed, which allows for a more accurate comparative evaluation of the efficiency of coil heat exchangers based on springtwisted channels. THE PURPOSE. Carrying out calculations of coil heat exchangers of the "pipe in a pipe" type with a variable bending radius of a helical spiral based on spring-twisted channels and evaluating the energy efficiency of such devices in comparison with smooth-walled analogues. OBJECT of this study is a conical apparatus with coaxially mounted coil tubes. In this case, the inner tube is made in the form of a spring-twisted channel of circular cross-section, and the outer one is made of smooth pipe. METHODS . As part of the work, the engineering calculation of the conical coil apparatus has been adjusted, based on theoretical research and solving the related heat exchange problem, and includes the equations of the modified Ieshke correction factor, criterion equations for calculating heat exchange with heated (hot) and heated (cold) water, and the determination of heat transfer and heat transfer coefficients through the heat exchange surface. RESULTS . In a coil heat exchanger with spring-wound pipes, the temperature of the heated coolant is 8.88°C (60.98°C versus 52.1°C) higher than in smooth-walled pipes. The thermal efficiency of such structures is higher: the power is 25.6 kW at a drop of 20.7°C versus 23.5 kW and 20.4°C, respectively. Heat transfer coefficient of spring-twisted pipes (1543 W/(m2·K)) higher due to turbulence and secondary flows. Hydrodynamic analysis shows a reduction in the cost of pumping heat carriers based on springtwisted channels to 1,438 Watts compared with 1,590 watts for smooth-walled structures. This is due to the shorter required length of the heat exchange element. The superiority of spring-twisted channels is confirmed by a higher value of the Kirpichev criterion (17,83) compared to smoothwalled analogues (14,77), which characterizes their improved energy performance. CONCLUSION . Calculations of coil heat exchangers of the "pipe in a pipe" type with a variable bending radius of the spiral were carried out on the basis of two variants of heat exchange elements: a spring-twisted channel and a smooth pipe, the data obtained are consistent with the results of mathematical modeling. The results of the calculation confirm the technical and energy feasibility of replacing smooth tubes with spring-twisted tubes in the designs of heat exchangers. This modification makes it possible to simultaneously increase the thermal performance of the system and reduce the operational energy consumption for moving the coolant, which leads to a significant increase in the overall energy efficiency of the system. Thus, the use of spring-wound elements in heat exchangers is an innovative solution that improves the efficiency and reliability of heat exchange technology.